Correctly handle the "multiple string tables" case for string resolution in the dynamic section

The index of the string table section used to resolve various strings in the
dynamic section is given by the sh_link field in the dynamic section header.
As several string tables with the same name can co-exist in an elf file
we must explicitely look for this specific string table instead of
looking for the first string table in the file.
Merge pull request #10 from yannrouillard/multiple-stringtables-fix

Correctly handle the "multiple string tables" case for string resolution...